1. Field of the Invention
The present invention relates to preparation and use of novel polymeric organofluorosilicon compounds and their corresponding aqueous emulsions to impart water and oil repellent properties to substrates coated therewith. More specifically, this invention relates to hydrophobic and oleophobic polymeric fluorocarbon siloxanes and emulsions thereof.
2. Description of the related art
It is known that hydrolyzable silanes can be formulated as aqueous solutions or emulsions that can be applied to various substrates to impart hydrophobic or water repellency properties. However, for these emulsions to achieve long term storage stability they must be buffered to specific pH ranges to inhibit or prevent the hydrolysis of the silanes in the aqueous medium (see for example, U.S. Pat. No. 4,990,377 and U.S. Pat. No. 4,877,654). It is also known that when hydrolyzable fluorocarbon silanes are applied to various surfaces, they can impart both water repellency and oil repellency to those substrates. However, those hydrolyzable fluorocarbon silanes are usually applied to surfaces in the molten state or dissolved in volatile organic solvents, and must generally be cured by heating with a catalyst to chemically affix the fluorocarbon silane to the substrates (U.S. Pat. No. 3,012,006). The use of such volatile solvents are generally harmful to the environment and may be hazardous due to their flammability. Where aqueous solutions or emulsions of the hydrolyzable fluorocarbon silanes are possible, the formulations cannot be stored for long periods of time, especially under a broad range of pH conditions, without undergoing hydrolysis and self-condensation to form water insoluble polymeric structures.
It is generally recognized (see, Silane Coupling Agents, E. P Plueddemann, 2 nd. Edition, Plenum Press, N.Y., 1991; and Silanes And Surfaces, D. E. Leyton, Gordon and Breach Science Publ., NY, 1986) that an important aspect of the durable oil and water repellency that is imparted to surfaces by hydrolyzable fluorocarbon silanes, such as with fluorocarbon alkoxysilanes, is the chemical bonding that occurs between the silane and the active hydrogen functional groups on the substrate. This is achieved by initial hydrolysis of the hydrolyzable groups on the silane to silanol groups, which then undergo condensation with the functionality on the substrate. The more hydrolyzable groups there are in the fluorocarbon silane to bond with the substrate, the more durable the coating will be. The normal method of achieving maximum bonding sites is to use a silane containing the maximum hydrolyzable groups on the silicon atom, which is three.